In the field of mass spectrometry, there is not an ion source which can respond to all of requests. Therefore, various ionization methods such as corona discharge ionization and glow discharge ionization have been developed. References related to the present invention which uses dielectric barrier discharge or light are introduced.
U.S. Unexamined Patent Application Publication No. 2011/0042560 describes an ionization method using dielectric barrier discharge. According to the method, samples are ionized by irradiating a sample with a plasma generated by the dielectric barrier discharge. First, a discharge gas is introduced into a discharge area. The introduced discharge gas is converted into a plasma by the dielectric barrier discharge. The sample is irradiated with the generated plasma gas by an electric field or a pressure to ionize the sample. The dielectric barrier discharge used in this example generates a plasma in which a temperature of neutral molecules or ions is lower than a temperature of electrons. The plasma is referred to as a low temperature plasma and is featured in that samples are ionized with less fragmentation.
International Publication No. WO2011/089912 describes an ionization method using a dielectric barrier discharge under a reduced pressure. A pressure of an ion source is reduced, and therefore, it is not necessary to provide a capillary having a small conductance between the ion source and a mass spectrometry unit even in a case where a sample is prepared under an atmospheric pressure as in an atmospheric pressure chemical ionization method. Therefore, a loss of ions is reduced when ions are introduced from the ion source to the mass spectrometry unit, and a highly sensitive analysis can be carried out. Also, since the dielectric barrier discharge is used, a fragmentation of molecule ions is more restrained than in a glow discharge under a reduced pressure.
U.S. Pat. No. 7,109,476 describes a method of combining plural ionization methods to be used for an ion source of a mass spectrometer. The ionization methods are an atmospheric pressure photoionization method, an atmospheric pressure chemical ionization method, and an electrospray ionization method. According to the example, a method of continuously switching the ion sources or simultaneously operating the ion sources in analysis is described.
U.S. Pat. No. 7,196,325 describes a method of combining to use an ionization using a photoelectron and an ionization by glow discharge at an ion source of a mass spectrometer. The plural ion sources are operated separately or simultaneously in analysis. Particularly, according to the example, an emitter of a photoelectron is installed at a glow discharge area, and an method of a photoelectron induced electron ionization using the configuration is described. The method is that low energy photoelectrons are accelerated between electrodes for glow discharge and that samples are ionized by the electron.
Japanese Unexamined Patent Application Publication No. 2011-117854 describes a discharge ionization current detector mounted with an illumination as a current detector for a gas chromatograph. According to the example, an amount of ions generated by a dielectric barrier discharge by using a current detector is measured. The illumination installed at an ionization source unit plays a role of lowering a breakdown voltage of the dielectric barrier discharge by an irradiation of light. When the discharge is started, the discharge is continued by applying a discharge maintaining voltage which is lower than an ordinary breakdown voltage on electrodes, and a stable plasma is formed. Therefore, life of the illumination can be prolonged by switching off the illumination after starting the discharge.